During selection of filter bag media, basic parameters taken into consideration are
1. inlet gas temperature, 2. % moisture contents in flue gasses , inlet dust load & it’s characteristics.
Normally for all types of non woven bags, cleaning pressure of 5-7 kg/cm2 to be kept.[ It also depends on bag length & dia ],For non woven membrane bags, glass or glass with membrane bags cleaning pressure should be in between 3-3.5 kg/cm2.
If pressure in both cases will be more than above mentioned values then bags will get less life & chances of pre-mature failure or carry over of fine dust in bag filter, results into high DP.
DP mode, it is “ on demand “ cleaning of bags. When DP across bag filter increases to it’s set upper limit, cleaning will start & when DP drops down below set limit then cleaning will stop.
In time mode, it is continuous & cleaning program will start as soon as bag filter will be in operation.
In DP mode, bag life will enhance, as compare to time mode.
All membrane non woven & woven fabric bags operates on a principle of surface filtration where micro fine particles will not pass through membrane lamination hence nearly zero emission.
Moreover, membrane laminated bags will require less pressure as compare to conventional fabric media bags , so less mechanical stress or flexing of fabric hence more bag life.
Any new bag when it is installed should be pre-coated. This will protect mother fabric from unwanted chemical reaction of gases generated in process. A fine pre-coat layer of dust over bag surface is a main reason of developing dust cake over the bag.
In some cases, it is not practically possible to pre-coat bags by external dust. In such cases, installed bags can be pre- coated with dust which is a process dust generated during operation of bag filter. So unless pressure drop across bag filter reaches to 100 mmWC, then only cleaning cycle programmer to be started.
When DP of bag filter is beyond 150 mmWC, then it is consider HIGH DP. The main reasons of high DP is either sudden increase of inlet dust load or gas flow handled by bag filter is more than design flow or generation of fines are more in inlet dust or ineffective cleaning of bags due to wrong cleaning program timing settings.
When pollution control board requirements of emission less than 30 mg/nm3 or in process fine particles less than 5 microns size are more than 15 % .
Any failure of bag, categories under three sections 1. Failure due to mechanical 2 failure due to long lasted excessive / surge temperature 3. Fabric chemically reacted with sudden changes in process gas composition.
IFF is having well equipped test lab and R & D center facility to find out and pin point root cause with conclusion . We can also tell you residual bag life left.